Aspects of the present invention relates to performance and safety characterization or assessment systems and processes. In particular embodiments of the invention are directed to apparatus and methods for safety and performance characterization capable of operating before, during, and after a destructive event from a system or item under test.
Calorimetry can include processes of measuring an amount of heat released or absorbed during a chemical reaction. Calorimetry can be used in a wide range of material analysis across multiple industries. An Accelerating Rate calorimeter (ARC) method is one method used where a material sample is placed within an oven type enclosure. Temperature within the enclosure is elevated through multiple step increases with rest periods at each step. This increase continues until the sample reaches a thermal runaway condition where the heat release of the sample can be recorded.
For battery characterization the ARC methodology is questionable as the increasing heat may not be representative of real world conditions and may impact data collection. Lithium battery heat generation, as it approaches thermal runaway, is of interest as well as what occurs during the event.
A new approach can include use of isothermal calorimetry methodology where the cell's ambient temperature is controlled tightly during actual testing. This exemplary approach allows for an accurate evaluation of heat generated from chemical reactions or physical changes occurring within the cell. A goal can include use of various embodiments of the invention to evaluate isothermal calorimetry as a potential method for characterizing the potential energy release during a destructive event, the impact to surrounding environment, and risk mitigation development.
According to an illustrative embodiment of the present disclosure, embodiments of the invention include exemplary processes and associated equipment to adapt or construct a heat flow calorimeter to accept a sealed pressure vessel. In some embodiments, an apparatus is provided that combines a robust sample environment of a closed bomb (to enable overcharge, burn, detonation, etc of any sample in the closed bomb) with a highly sensitive detection capability including heat flow calorimetry. In particular, some embodiments have been constructed containing a pressure vessel in a sample chamber of the calorimeter for sample materials that would then be forced fully through decomposition. In some embodiments, an exemplary system included a pressure vessel and a capacity for deliberate overcharging of Lithium containing batteries in order to determine resulting pressure and heat energy released.
Also, efforts to obtain increased energy density of battery cells highlight a need for electrochemical techniques as well as additional characterization methods for these cells in order to meet user needs and safety requirements. In particular, a continuing need has called forth inventive efforts for developing novel calorimeters to satisfy various requirements for requiring activities including high energy density systems such as chemical energy storage systems, propellant, explosive, and pyrotechnic devices. To support optimization of electro chemical energy storage systems in particular it is necessary to understand their thermal characteristics at rest and under prescribed charge and discharge cycles. In one example, a need existed to develop a calorimeter system able to accommodate multiple battery cell configurations and provide empirical system data for use in modeling and simulation. Heat capacity, and thermal efficiency for each battery cell were determined, as well as the actual heat load from each surface of the cell. The heat flow from each of six surfaces of the cell and overall thermal efficiency were obtained with the cell at rest and under a variety of prescribed charge and discharge cycles representative of typical usage of these cells. Testing was completed isothermally at 25° C. to capture the requirements necessary to remove the entire generated thermal load from the battery cell. Moreover, these needs also included a requirement to create testing systems which are capable of larger testing capabilities that necessarily include a need to use larger systems, create more testing options with respect to samples under test, and create an ability to more cost effectively repair or replace costly components in such test systems which existing systems do not accommodate in a cost or time effective manner. As systems are scaled up in size, there is a higher level of failures in system components which require new designs to accommodate repairs or maintenance rather than throwing out large sub-assemblies. Also, there is a need to be able to swap out components for greater customized design or configurability of testing systems with respect to desired testing processes or data collection.
As an example of one embodiment, an improved measuring cell for a temperature bath was designed and constructed to measure the heat flow of larger cells (e.g., 18×8×16 cm). Heat flows from 0.01 to 7.00 Watts were measured with an average signal noise less than 1 mW. In one example, heat capacities of samples were also determined with experimental deviation of less than 2%.
Embodiments of the invention can include apparatus and methods for providing flexible and repairable testing capabilities for systems that generate or absorb heat such as energy storage systems. One embodiment can include a temperature bath structure adapted to contain and maintain a fluid bath at a predetermined temperature, an outer containment structure adapted to insert into the temperature bath structure, heat sinks, thermal sensor assemblies, an internal containment structure, and thermal barriers between different elements of the invention to isolate different sections from each other. An embodiment of the invention can include a system where the thermal sensor assemblies and heat sinks removeably attach to different sections of the inner containment structure so as to measure heat flow into or out of the inner containment structure's different sections without being altered by direct thermal contact with other inner containment sections. Embodiments of the invention permits rapid insertion/removal of samples as well as replacement of sections of an exemplary system including embodiments or parts of the thermal sensor assemblies as well as providing an ability to obtain separate thermal measurements associated with different sections of a sample under test within the inner containment structure. Other aspects of the invention include a capability to insert or substitute existing components such as containment structure elements, thermal sensors etc. with different sized elements or structures to accommodate different types of samples or differently sized samples under test. Embodiments can include electrical bus or wiring structures such as separate wiring sections and quick disconnects that also permit rapid repairs or alteration of configurations of various aspects of embodiments of the invention.
Existing systems do not provide a needed capability in a variety of areas including chemical battery testing. For example, existing systems might provide the closed bomb and low sensitivity or alternatively heat flow sensitivity but much stricter sample environment but not a combination thereof.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.